4 Answers
4

No, the "default" apps on the bottom row aren't the only apps that can receive push notifications or display number badges.

There isn't necessarily a relationship between push notifications and number badges. Apps can have number badges without push notifications (Mint comes to mind) and can have push notifications without number badges (MLB At Bat, for example).

You can actually change which apps are on the Dock (bottom bar) to whatever you like. And various apps have the new event count. For instance, I use The AT&T MyWireless app, and when my bill is due, I get a push notification there as well. Also when your apps have updates, you'll get one from the App Store icon. Any application that supports notifications will get a badge.